In complementary bipolar technologies for high-precision high speed analog and mixed-signal applications, a sinker contact is generally used to reduce the collector resistance. In a standard process integration sequence, collector sinkers are realized by using high-energy ion implantation of p-type or n-type dopants into the collector epitaxy. Dopant activation and diffusion are then realized by a thermal step (e.g., furnace or rapid thermal anneal). The diffusion penetrates into the collector epitaxial layer to electrically contact the underlying buried layer.
One or two lithographic steps are necessary to selectively introduce dopants into the collector epitaxy. Furthermore, high-energy high-dose ion implant capability is used for higher voltage applications in which thick collector epitaxy is used to guarantee high breakdown characteristics.